1. Field of the Invention
The present invention relates generally to apparatus for collecting, storing, and transmitting solar heat, and more particularly to apparatus for directly heating water including means to prevent freezing of the water contained within the solar collector.
2. Description of the Prior Art
The desirability of utilizing solar energy for heating purposes and for domestic hot water have long been recognized. Systems for both heating and providing domestic hot water primarily utilize air or a liquid anti-freeze for transference of heat from the solar collector to a storage tank. In such systems, a heat exchange system is needed to transfer the heat from the air or liquid to the water to be used. The cost and potentially dangerous problem of water contamination have resulted in more recently developed systems wherein water is circulated through the collector and the problems associated with the heat exchanger are eliminated. Most recent efforts in this regard are typified by U.S. Pat. No. 4,044,754 to Cronin, et al; U.S. Pat. No. 3,989,032 to Harrison; and U.S. Pat. No. 3,986,049 to Schlesinger. Cronin teaches apparatus for draining the collector to prevent freezing. Harrison teaches uses of an inflatable member which is collapsible to prevent bursting of tubes in the metal collector and Schlesinger teaches circulation of previously stored hot water or water heated by an electric heater to prevent freezing of the water in the collector. Such systems often result in extended periods of non-use of the solar collector and result in loss of heat already stored to prevent freezing of the water within the collector.